A panel of geriatric clinical experts rated problems in pharmacologic management as the most important target for improvement of care in vulnerable older people. People aged 65 years or older have the highest age-specific drug consumption rates, yet abundant evidence indicates that they commonly do not receive appropriate drug treatment for a wide variety of conditions. In particular, older persons with complex chronic diseases appear to have a reduced likelihood of receiving preventive drug treatment for unrelated diseases. This application aims to conduct large-scale, longitudinal, observational studies of determinants of initiation and persistence of use of preventive drugs in older people. A particular focus is on the impact of common, symptomatic conditions, including depression, Parkinson disease, and chronic obstructive lung disease, on use of preventive therapies, including glaucoma drugs, bone resorption agents, and lipid-lowering drugs. Another evaluation will consider the relative use of drugs in the last year of life. Additional methodological aims will quantify the clustering of drug use within prescribers and evaluate alternative reference groups for studies of new users of specific medication classes. Studies will utilize administrative claims data from two large populations of persons aged 65 years or older: 1) over 500,000 older residents of Pennsylvania who had prescription drug coverage through that state's Pharmacy Assistance Contract for the Elderly (PACE) program between the years 1994 and 2005; and 2) all residents of British Columbia, including over 500,000 persons during the years 1995-2005, who received prescription benefits through that province's Pharmacare program. Data sources for these populations include: drug claims for all filled prescriptions; data on hospitalizations and outpatient visits including diagnoses; demographic information on patients and their prescribers; and information on program eligibility and mortality. These populations include large numbers of persons at particular risk for under-treatment including those aged 85 and above, women, blacks and those with multiple morbidities. Data analysis will use methods for longitudinal and clustered data to account for repeat prescriptions in the same people and to characterize the clustering of patients within prescribers. These studies are intended to advance methodologic strategies for evaluation of drug use and its effects in older people and to lay the foundation for interventions to improve prescribing in this population. [unreadable] [unreadable] [unreadable] [unreadable]